Oil or gas is obtained from a subterranean formation by drilling a wellbore that penetrates a hydrocarbon-bearing formation. It is desirable to maximize both the rate of flow and the overall amount of flow of hydrocarbon from the subterranean formation to the surface.
One way that the rate of hydrocarbon flow and the overall amount of hydrocarbon flow can be reduced is by fines production or sand migration in the formation or by precipitation. The relatively high velocity in the permeable matrix of the subterranean formation near the wellbore is sometimes sufficient to mobilize particulates. These particulates can be carried and then plug flow channels in the formation, a proppant pack, or a gravel pack. It is desirable to minimize fines or sand migration, since such particulates block flow paths, choking the potential production of the well. In addition, such particulates can damage downhole and surface equipment, such as screens, pumps, flow lines, storage facilities, etc.
After most acidizing treatments, the well production often declines drastically with time, which is mainly due to formation of fines and fines migration. Formation of fines and their movement is usually worse and accelerated after an acidizing treatment. Hence, the locking of fines is essential to maintain well productivity for a longer period of time, especially after an acidizing treatment.
For example, if hydrofluoric acid is used, the reaction of the hydrofluoric acid (HF) may react with clay, other aluminosilicate mineral, silica, or quartz. New fines may be released as a result of partial reaction with high surface area minerals. A non-dissolved portion of the mineral can be released as a fine particle. In some cases, the rate of the acidizing reactions are so fast that the near-wellbore region within about 1 foot (0.3 m) may become poorly consolidated or unconsolidated. Fines migration after an HF acidizing treatment can be especially problematic where kaolinite and illite clays are present. These clays are loosely bound and can be easily dispersed by production velocities near the well bore.
Similarly, in acidizing of a carbonate formation with any type of acid, non-carbonate fines can be released from the formation.
Such newly released fines can plug the pore throats of the formation, gravel packs, or mechanical screens to reduce permeability.
In addition, wellbores often penetrate subterranean formations that contain naturally unconsolidated particulates that may migrate when oil, gas, water, or other fluids are produced or flowed back from the subterranean formation.
Devices such as screens and slotted liners are often used to provide support for these unconsolidated formations to inhibit formation collapse. Usually, the annulus around the support device is gravel packed to reduce the presence of voids between the device and the borehole. Typically, such gravel packing operations involve the pumping and placement of a quantity of a desired size of particulate material into the annulus between the tubular device and the borehole of the wellbore. Gravel packing forms a filtration bed near the wellbore that acts as a physical barrier to the transport of unconsolidated formation fines with the production of hydrocarbons. These support devices provide support for the wellbore and gravel packing and prevent some fines from entering the hydrocarbon flow into the well.
Some types of screens are adapted to be expanded to contact the wellbore wall either with or without gravel packing. It is however, impossible to eliminate all voids between the screen and the wellbore wall. Fines fill these voids blocking flow and in some instances fines flowing through these voids erode the screen destroying its effectiveness.
One common type of gravel packing operation involves placing a gravel pack screen in the wellbore and packing the surrounding annulus between the screen and the wellbore with gravel of a specific mesh size designed to prevent the passage of formation sand or fines. The gravel pack screen is generally a filter assembly used to retain the gravel placed during gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel pack sand. Similarly, a wide range of gravel sizes is available to suit the characteristics of the unconsolidated or poorly consolidated particulates in the subterranean formation. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow.
Gravel packs can be time consuming and expensive to install. Due to the time and expense needed, it is sometimes desirable to place a screen without the gravel and, particularly in cases in which an expandable screen is being placed, it may be unrealistic to place a bed of gravel between the expandable screen and the wellbore. Even in circumstances in which it is practical to place a screen without a gravel pack, it is often difficult to determine an appropriate screen size to use as formation sands tend to have a wide distribution of sand grain sizes. When small quantities of sand are allowed to flow through a screen, screen erosion becomes a significant concern. As a result, the placement of gravel as well as the screen is often necessary to control the formation sands.
An expandable screen is often installed to maintain the diameter of the wellbore for ease of access at a later time by eliminating installation of conventional screens, gravel placement, and other equipment. However, the ability to provide universal screen mesh that can handle wide particle size distribution of formation sand is unrealistic, if not impossible.
Another method used to control particulates in unconsolidated formations involves consolidating a subterranean producing zone into hard, permeable masses. Such consolidation of a subterranean formation zone often involves applying a resin followed by a spacer fluid and then a catalyst. As used herein, the term “resin” refers to any of a number of physically similar polymerized synthetics or chemically modified natural resins including thermoplastic materials and thermosetting materials. Such resin application may be problematic when, for example, an insufficient amount of spacer fluid is used between the application of the resin and the application of the external catalyst. The resin may come into contact with the external catalyst in the wellbore itself rather than in the unconsolidated subterranean producing zone. When resin is contacted with an external catalyst, an exothermic reaction occurs that may result in rapid polymerization, potentially damaging the formation by plugging the pore channels, halting pumping when the wellbore is plugged with solid material, or resulting in a downhole explosion as a result of the heat of polymerization. Also, these conventional processes are not practical to treat long intervals of unconsolidated regions due to the difficulty in determining whether the entire interval has been successfully treated with both the resin and the external catalyst. Gravel packing is a costly operation and resin placement can sometimes damage the formation.
In addition to the unconsolidated formation sands often found in subterranean formations, particulate materials are often introduced into subterranean zones in conjunction with conductivity enhancing operations and sand control operations. Conductivity enhancing and sand control operations may be performed as individual treatments, or may be combined where desired.
Preventing formation sand and fines from migrating from an unconsolidated formation has always been a challenge. While previously known treatment methods for unconsolidated formations provide improved particulate control, multiple treatment steps that are time consuming and expensive are usually required.
Therefore, it is desirable to develop relatively simple and relatively inexpensive treatment compositions and methods to improve or maintain the rate of fluid flow while reducing particulate migration.